The invention relates to a profile edge of an aerodynamic profile.
Aerodynamic profiles are, for example, helicopter rotor blades. In forward flight the helicopter rotor blades experience fundamentally non-stationary flow conditions. In high-speed flight these may be very complex. Pronounced shock waves arise on the advancing rotor blade in this case. On the retreating rotor blade, on the other hand, non-stationary vortex separations occur in the course of high uplift. The latter phenomenon is described by the term "dynamic stall".
In the case of a helicopter rotor blade the angle of attack of the profile, for example, changes dynamically with the frequency of rotation of the rotor. This means that a different angle of attack applies for each azimuth angle of the rotor blade with respect to the longitudinal axis of the helicopter. In general, in the course of dynamic increase of the angle of attack, aerodynamic coefficients arise which are different from those within the range of dynamic reduction of the angle of attack. This results in aerodynamic hysteresis. By reason of the accelerated profile movement of the helicopter rotor-blade profile, in comparison with the static case a gain in uplift arises which can be utilized to good effect. Within the range of high angles of attack, however, the uplift collapses very considerably and rapidly, as a result of which a considerable rise in drag and in moment about the axis of rotation is generated. The moment is nose-heavy and loads the rotor blade in pulsed manner. It can stimulate the latter to oscillate.
With the aid of the so-called "droop nose" it is known to reduce the increase in drag and also the moment that has a considerably nose-heavy effect. The "droop nose" is a leading edge of the rotor blades that is variable in shape. The objective of this variable leading edge is a selective, cyclic decrease or increase in the curvature--operating with the rotation of the rotor--of the profile of the rotor blade with a view to improving the aerodynamic characteristics of the latter. Above all, the effects of the non-stationary separation of flow (dynamic stall) can be influenced positively with the "droop nose".
The collapse of the uplift and the associated effect of, for example, drag rise (rise in drag as a consequence of transonic flow in the region of the blade tip--advancing blade, psi.tbd..dwnarw..epsilon..degree.), fluttering, etc may be shifted to higher angles of attack by this means.
Actuators are known in the aircraft domain for adjusting parts of the aerofoils. Such actuators are, for example, electric motors, pneumatic drives or, as in U.S. Pat. No. 4,296,900, hydraulic drives, or, as in U.S. Pat. No. 4,922,096, piezoelectric actuators which are arranged under the outer skin and which change the contour thereof by local application. These local measures are still not optimal and in some applications also cannot be achieved.
DE 40 33 091 C1 proposes the attainment, through the use of electrostrictive structures comprehensively, of an optimisable elasticity behavior of wing contours, use being made of matrices consisting of ceramic material. A change of wing shapes is not provided for.
The object underlying the invention is to create a transformation, in terms of structural mechanics, of the effects of the "droop nose" in the case of a profile edge of an aerodynamic profile.
This object is achieved by means of a profile edge with an aerodynamic profile wherein the profile edge comprises multifunctional material on its outside and/or inside or within its structure, wherein a coating or a shear-active layer of multifunctional material integrated within the structure of the aerodynamic profile is provided in partly distributed manner on the profile edge, and wherein flexural moments and/or longitudinal or thrust forces which generate a deformation of the structure can be introduced into the structure forming the profile edge by means of the layers of multifunctional material as active layers.
Further developments of the invention are defined in the subclaims. As a result, a deformation of the profile edge of the aerodynamic profile can be generated that conforms to the aeroelastic requirements. Conventional actuators--for example, electric motors or pneumatic or hydraulic drives--are, by virtue of their dimensions, too large and too heavy to be capable of being integrated within a profile edge, of a helicopter rotor blade for example. On the other hand, the provision according to the invention of multifunctional materials proves to be advantageous not only by virtue of their dimensions and their weight but also by reason of their suitability for highly dynamic applications. The performance data of the conventional known actuators, such as electric motors, pneumatic drives or hydraulic drives, often prove to be too low and therefore unsuitable for use with a view to transformation, in terms of structural dynamics, of the so-called "droop nose" on rotor blades; piezoelectric actuators acting locally are unable to bring about the global deformations of the entire rotor blade under consideration that can be achieved in accordance with the invention.
In principle a profile edge of an aerodynamic profile is created wherein the profile edge comprises multifunctional material on its outside and/or inside or within its structure. A coating of multifunctional material is preferably provided in partly distributed manner on the profile edge. In this connection the profile edge is advantageously a leading edge of a rotor blade, for example. However, the multifunctional material may alternatively also be a shear-active layer integrated within the structure of the aerodynamic profile. By means of the multifunctional material, flexural moments and/or longitudinal or thrust forces can be introduced into the structure forming the profile edge. A deformation of the structure can be generated by this means. Drive of the multifunctional material can be effected selectively and variably over the periphery of the aerodynamic profile. This drive may be effected either in phase or in antiphase. Sensors consisting of multifunctional material and adaptive regulators are preferably also provided. By this means the actual deformation of the profile edge can be detected by the sensors and compared in the adaptive regulator with predetermined desired values. A deviation of the actual value from the desired value can be regulated by the adaptive regulator through appropriate response of the multifunctional material by way of actuator. In particularly preferred manner the multifunctional material that is provided by way of actuator serves at the same time as sensor for the profile-edge deformation.
In particularly preferred manner the profile edge is constructed with a wall thickness that is variable over the periphery. This stiffness which is variable over the periphery of the structure of the aerodynamic profile then permits an additional passive influence to be exerted on the profile-edge deformation which arises.
By way of multifunctional material use is preferably made of a material that is suitable for high-frequency applications. In particularly preferred manner use is made for this purpose of a piezoceramic, an electrostrictive material or a magnetostrictive material. The profile edge preferably consists of fibre composite material, in particular of composite material reinforced with carbon fibre (CFC) or composite material reinforced with graphite fibre (GFC). But it may also consist of metal. The active layers consisting of multifunctional material are preferably laminated or bonded onto the profile edge or applied by means of plasma processes. But they may also be applied by alternative processes or, preferably, incorporated into the outermost layers by lamination. In the latter case a thin layer of glass fibre can be applied by way of protective layer, having a layer thickness of 10 .mu.m for example, over the layer incorporated by lamination. If the multifunctional material is provided in the form of a shear-active layer it is preferably embedded into the structure of the profile edge of the aerodynamic profile or incorporated by lamination.
The profile edge may be either a leading edge or a trailing edge. For example, it is part of a helicopter rotor blade, part of a vane of a wind-power installation, part of a turbine blade or compressor blade or part of an aerofoil of an aircraft.
If the profile edge is provided by way of elastic trailing edge of an aerodynamic profile, a trailing edge tapering to a point is preferably provided. Hence a variable curvature of aerodynamic profiles can preferably be generated.